1. Field of the Invention
The present invention relates to a spacecraft having a solar array and an articulation device for adjusting the position of the solar array relative to the spacecraft. The present invention further relates to a method for deployment of the articulated solar array.
2. Description of the Prior Art
Orbiting spacecraft, such as satellites, have previously employed articulated solar arrays, the position of which could be adjusted to track the sun, and thereby, by maximize electrical power generation. Typically, the position of such articulated solar arrays was adjusted by means of articulation devices, such as gimbals, which permitted rotation of the arrays about two orthogonal axes. A first gimbal permitted rotation about an axis normal to the surface of the spacecraft. This first gimbal was generally employed to track the sun as the spacecraft moved along its orbital flight path. This is often referred to as alpha tracking. A second gimbal permitted rotation about an axis normal to the first gimbal axis and normal to the longitudinal axis of the array. The second gimbal was generally employed to track the sun as its position with respect to the orbital plane of the spacecraft changed with the seasons. This is often referred to as beta tracking. The first gimbal was typically located inboard of the second gimbal relative to the body of the spacecraft. This type of spacecraft operated with its solar arrays extended in a position such that the axis of the first gimbal was aligned normal to the orbital plane, rather than in the orbital plane, and with the longitudinal axis of the spacecraft aligned with the local vertical and pointing toward the earth. This flight mode allowed the first gimbal to rotate about its axis synchronously and phased with the orbital rate of the spacecraft so that the solar array would track the sun as the spacecraft moved along its flight path.
The previous methods for articulation of solar arrays allowed full tracking of the sun during all seasons, but produced products of inertia unfavorable to control of spacecraft attitude when the first gimbal was rotated following angular displacement of the second gimbal. Such effect would be produced regardless of the attitude of the spacecraft with respect to its orbital plane.
An additional drawback of these previous methods for articulation of solar arrays on spacecraft resulted from the fact that the solar arrays were rotated about the axis of the first gimbal aligned normal to the orbital plane in order to track the sun as the spacecraft moved along its orbital flight path. Since the solar arrays were aligned (i.e., edge-on) with the flight path for but a short time twice per obit, aerodynamic effects were produced that were unfavourable to control of attitude of the spacecraft and maintenance of its orbital altitude.